The present invention concerns a method for prospectively isolating and/or identifying mesenchymal stem cells.
The term “mesenchymal stem cells” (MSC) is not uniformly defined in the literature. In principle there are two distinct types of cells: MSC which are isolated directly from non-hematopoietic primary tissue (e.g. bone marrow, adipose tissue, placenta), and cells which differentiate in culture from these primary cells into adherent, fibroblast cells and there express cell surface markers, such as CD73, CD105, CD166, but are negative for the hematopoietic stem cell marker CD34 and the pan-leukocyte marker CD45. In general, cells generated in culture are known as mesenchymal stem cells, as after this process they themselves possess a multipotent capacity to differentiate. Just recently however the International Society for Cellular Therapy has brought out a position statement compiled with the aim of standardizing the nomenclature for these cells (Horwitz E M et al., “Clarification of the nomenclature for MSC: The International Society for Cellular Therapy Position Statement”, Cytotherapy 2005:7; 393-395). In this publication, cells from primary tissue that have the ability to form fibroblast colonies in culture (colony forming unit fibroblast=CFU-F) are described as mesenchymal stem cells (MSC). In contrast, adherent cells with fibroblastoid morphology which are generated by culturing cells from primary tissue are known as “multipotent mesenchymal stromal cells”. The acronym “MSC” has however likewise been retained for these cells.
Owing to their multipotency, i.e. their ability in suitable in vitro and in vivo conditions to differentiate into different mesenchymal tissues (such as bone, fat, muscle, cartilage, etc.), mesenchymal stem cells are already being used therapeutically. Thus for example, MSCs isolated from umbilical cord blood, bone marrow and adipose tissue that are capable of differentiation can be expanded in vitro and differentiated into osteoblasts, chondrocytes and myocytes, and then be used again in vivo for example for regenerating bones, cartilage, tendons, muscles and adipose tissue, as well as stroma.
Besides the ability to adhere rapidly and with stability to plastic or glass surfaces, MSC (multipotent mesenchymal stromal cell) phenotypes are characterized by their fibroblastoid morphology and by their expression (for example, of CD73, CD90, CD105, CD166) and/or lack of expression (of CD34, CD45). Many of the surface molecules expressed on MSC can also be found on endothelial and epithelial cells and on muscle cells. On the other hand, however, MSCs are clearly distinct from hematopoietic stem cells as they do not express any specific hematopoietic markers such as CD45, for example.